Although legacy (copper) wirelines have served as a principal information transport backbone for a variety of telecommunication networks, the continued development of other types of signal transport technologies, particularly those capable of relatively wideband service, including coaxial cable, fiber optic and wireless (e.g., radio) systems, have resulted in a multiplicity of systems that serve a diversity of environments and users. A particular advantage of wireless service is the fact that it is very flexible and not limited to serving only customers having access to existing or readily installable cable plants. Moreover, there are many environments, such as, but not limited to portable data terminal equipments (DTEs), where a digital wireless subsystem may be the only practical means of communication.
In order to provide digital communication service, the wireless (radio) subsystem must be interfaced with an existing digital network's infrastructure, which typically includes legacy wireline links (that may contain one or more repeaters) coupled to an incumbent service provider site. In addition, the digital radio site which provides access to the wireline must also provide a source of electrical power. In many environments, the required power supply is either not readily available, or its cost of installation is prohibitively expensive.
The invention described in co-pending U.S. patent application, Ser. No. 09/771,370, filed Jan. 25, 2001, by Eric Rives et al, entitled: “Loop-Powered T1 Radio” (hereinafter referred to as the '370 application), assigned to the assignee of the present application and the disclosure of which is incorporated herein, is directed to a loop-powered digital (T1) radio architecture that is configured to solve this lack of available local power problem by extracting power from the line. This effectively eliminates having to locate the radio where a separate dedicated power supply is either available or can be installed, so that the radio may used practically anywhere access to a powered wireline is available.
The radio itself may comprise a blue tooth (spread spectrum) digital radio associated with portable digital terminal equipment, such as a notebook computer, or a remote digital radio that terminates a separate powered wireline. Power for operating the radio is extracted from the loop via a line interface coupled to tip and ring portions of respective transmit and receive segments of a powered T1 wireline link. The line interface contains a DC—DC converter to scale down the span voltage to standard voltages used to power the radio's digital signaling and transceiver electronics.
As diagrammatically illustrated in FIG. 1, the radio proper has a transceiver 10 (e.g. one that is ‘blue tooth’-compatible), which performs modulation and up-conversion of baseband signals supplied from a data pump (T1 framer chip) 12 to an FCC-conformal band RF signal (e.g., a 2-6 GHz spread spectrum signal), for application via a first section of cable plant 14 to a first transceiver port 21 of a diplexer 20. The diplexer 20 has an (N-type) antenna port 23 coupled to an associated radio antenna 25. A second transceiver port 22 of the diplexer 20 is coupled via a second section of cable plant 15 to a receiver section of the transceiver, wherein the received RF signal is down-converted and demodulated to baseband for application to the data pump. The respective transmit and receive frequencies interfaced by the diplexer 20 with the antenna 25 are prescribed by one of two complementary frequency plans, the other of which is employed by a companion radio at a remote site.
To facilitate selectivity of either frequency plan, the radio transceiver—diplexer arrangement is preferably configured in the manner described in the U.S. Pat. to P. Nelson et al, U.S. Pat. No. 6,178,312, issued Jan. 23, 2001, entitled: “Mechanism for Automatically Tuning Transceiver Frequency Synthesizer to Frequency of Transmit/Receiver Fitler” (hereinafter referred to as the '312 Patent), assigned to the assignee of the present application and the disclosure of which is incorporated herein. As shown and described therein, the frequency plan (transmit/receive frequency pair) of the radio is defined by selectively coupling the appropriate one of two diplexer ports of a diplexer unit to the transmit port of the transceiver and the other diplexer port to the receive port of the transceiver. (At the far end or remote site the diplexer to transceiver port connections would be reversed.)
Because the sections of RF cable through which these diplexer-to-transceiver connections are made are lossy (e.g., 1-2 dB of insertion loss), special purpose, relatively fragile, and take up space within the radio's housing, they are installed by a skilled technician during assembly of the radio in accordance with the intended frequency plan of the equipment. As a consequence, should it be necessary to change the frequency plan of the radio in the field, it is customary practice to ‘swap out’ both units at opposite ends of the radio link, and the radios returned to the equipment supplier for refurbishment.